The present invention relates generally to a supercooling-prevention type or supercooling type heat storage apparatus having a latent heat storage material for use in warming systems, heat retaining systems, heating systems and so on.
Latent heat storage materials are being used in hot-water supply and heating applications because they have advantages of accumulating great amount of heat per unit of weight and constant heat output. In practical use, the heat storage material is divided into a number of portions which are in turn encased in a number of small bags. This is for preventing deviation of the heat storage material, for makinng constant the thickness of the apparatus to improve heating (heat storage) efficiency and, for use in a warming system, to provide flexibility for human wear. One example of conventional heat storage apparatus used in a heating system will hereinbelow be described with reference to FIGS. 1 and 2. In FIGS. 1 and 2, a heat storage apparatus 1 has a number of small chambers 2 communicated with each other and a heating wire 3 provided for the small chambers 2 such that the lengths of the heating wire 3 for the respective smaller chambers 2 are equal to each other. The heat storage is effected by dissolution of the heat storage material resulting from energization of the heating wire 3. For use as a heating system, the heating wire 3 is covered by a thermal insulating material 6 as shown in FIG. 2 and each of the small chambers 2 encases a latent heat storage material 4 and a supercooling-prevention material 5 for avoiding the supercooling of the latent heat storage material 4. In the conventional apparatus, the control of the heat storage to a constant temperature is made by the energization and deenergization of the heating wire 3 and may be continued after the heat storage in some cases.
One important problem in the conventional arrangement is, however, that the temperatures in the small chambers 2 vary depending on the located positions, that is, variations in temperature occurring among the small chambers 2 have a wide distribution. Since the supercooling-prevention material 5 does not act when the temperature exceeds its heat resisting temperature, it is required that the heating wire 3 is controlled so that the heating temperature is above the melting point .theta.1 of the latent heat storage material 4 and below the heat resisting temperature .theta.2 of the supercooling-prevention material 5. This temperature range (.theta.2-.theta.1) is not wide. For example, if sodium acetate trihydrate is used as the latent heat storage material 4 and sodium pyrophosphate decahydrate is used as the supercooling-prevention material 5, the melting point .theta.1 is 58.degree. C. and the heat resisting temperature .theta.2 is 80.degree. C., that is, the range is about 20.degree. C. Therefore, with the temperature variation of the heat storage apparatus widely occurring, some temperatures exceed the range. To avoid going outside the range, it would be required that the heating wire 3 is controlled so that the temperature is gradually increased, resulting in a long time being taken for the heat storage. Furthermore, the temperature of the latent heat storage material 4 in the small chambers 2 covered by a thermal insulating member increases during the heat storage. In the case that a thermostat is used for detection of the temperature, when the small chambers 2 covered by the heat insulating member are in the vicinity of the thermostat, the temperature can be detected thereby. However, the temperatures of the small chambers 2 apart therefrom are difficult to detect and thus the temperatures of the farther small chambers 2 further increases. To increase the number of the thermostats is not desirable in practice. Although it is possible to use a temperature detecting wire as the temperature detecting device, the temperature detecting wire is difficult to partially detect the variations of temperatures. Thus, the temperature of some of the latent heat storage material 4 increases and exceeds the heat resisting temperature .theta.2 of the supercooling-prevention material 5. During the discharge of heat of the latent heat storage material 4, even if the temperature becomes below the melting point .theta.1, the supercooling phenomenon in which the latent heat is not discharged occurs.
The above description has been made in terms of an apparatus having heat storage material for allowing the prevention of supercooling wherein the heat storage material discharges heat in response to the termination of the heat storage and it is impossible to discharge the heat when required. Therefore, attempts to allow the discharge of heat when required have been made hitherto and one example of such techniques is disclosed in Japanese Patent Provisional Publication No. 61-14283 wherein a supercooling type heat storage material is used. However, although the supercooling type heat storage material is liquid during the heat storage or supercooling, it is turned into a solid after heat discharge, resulting in loss of flexibility. The technique to resolve this problem is disclosed in Japanese Utility Model Provisional Publication No. 57-87276 or 57-85154 wherein a plurality of small chambers is defined by a flexible sheet and a heat storage material is encased in the small chambers so that flexibility is provided by the turns of the coupling portions of the small chambers. However, the supercooling heat storage material requires a means for collapsing the supercooling to discharge heat as disclosed in Japanese Patent Provisional Publication No. 61-14283, 61-22194 or 60-1020. The Japanese Patent Provisional Publication No. 61-14283 discloses a supercooling-allowable heat storage component comprising hydroxylpropylated gua-gum. The heat storage component is supercooled in a glass bottle and, when heat is required, a seed crystal is put therein or the heat storage component is stimulated by a metallic bar so as to collapse the supercooling to derive heat. The end of the metallic bar is sharp and therefore there is a safety problem. Furthermore, the heat storage component is apt to be leaked during the opening and closing of the vessel. The Japanese Patent Provisional Publication No. 61-22194 discloses a thermal energy storage device comprising an energy storage member and a stimulating member. The stimulating member comprising a seed crystal is brought into contact with the energy storage member which is in a supercooling state so that the supercooling is collapsed to derive heat energy. However, this device requires a means for providing the thermal insulation to avoid the melting of the seed crystal. The provision of the means makes the device large. Furthermore, the Japanese Patent Provisional Publication discloses a method wherein a bendable active strip encased in a receptacle is bent to collapse the supercooling state. However, a bending stress is frequently applied to the strip in response to the movement of the device, resulting in collapse of the supercooling when not required. In addition, it is actually difficult to provide such a stimulation means in each of the small chambers as disclosed in the Japanese Utility Model Provisional Publication Nos. 57-85154 and 57-87276.